$ { {-5} \times \left[\begin{array}{rr}{3} & {4} \\ {1} & {-1}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-5}\times{3} & {-5}\times{4} \\ {-5}\times{1} & {-5}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-15} & {-20} \\ {-5} & {5}\end{array}\right]}$